Yet I can think of someone who deserves very little privacy — a policeman making an arrest. Unfortunately, in some states it's a crime to make a video of a policeman doing just that. People recording police have been threatened, detained or arrested. Some were jailed overnight.

That's wrong. Police work for the public, they're paid with tax money, and most importantly, they have tremendous power. They've got the legal right to pull guns, detain us, lock us up and, in some cases, shoot us. The potential for abuse is great. So it's a good thing that modern video cameras are now so commonplace. Any abuse of police power in a public place is likely to be recorded. Why should that be a crime in some states?

I asked Radley Balko, an editor at Reason magazine who keeps an eye on issues like this: What's happened to the people who were arrested for videotaping cops at work?

"In most of these cases, the people aren't actually prosecuted," Balko said. "The charges tend to get dropped before these cases get to trial — I think because the people prosecuting these cases and the people who make the laws don't want the laws to actually get challenged. But it's a night in jail."

On what charge?

"In states that have these two-party consent laws, they rely on the old wiretapping laws. The claim is that police officers have a right to privacy while they're on the job in public exercising some pretty powerful responsibilities that we give them. I think that claim is ridiculous."

He says some authorities now claim that people who record the police while being arrested are "interfering with arrest or ... refusing to obey a lawful order, if they tell you to turn the camera off and you don't."

How does it interfere with the arrest?

"It's a ridiculous argument. But here's the thing: You may not go to jail for these charges. But they're going to take your camera, going to arrest you, you're going to be handcuffed, put in the back of a squad car. And nothing is going to happen to the police officers who illegally arrest you — usually."

Occasionally a cop caught abusing his power is arrested or fired. But that's rare.

In Maryland, motorcyclist Tony Graber got in trouble for recording a cop who pulled him over for speeding. Graber didn't know it was cop. He was just a guy in plainclothes with a gun. The cop eventually identified himself.

"Graber didn't get arrested until he posted that video on YouTube," Balko explained. "Once he posted it ... the state police raided his home — came into his home early in the morning, guns drawn — confiscated a bunch of computer equipment, held him and his parents at gunpoint, arrested him. He spent several nights in jail. He had felony charges hanging over his head until the case finally got to court."

Fortunately, a state judge threw out the charges and wrote a strong opinion:

"Those of us who are public officials and are entrusted with the power of the state should not expect our actions to be shielded from public observation."

He ended by asking, "Who watches the watchmen?" — a question Plato raised in "The Republic." Good for the judge. But Balko points out that no one punished the authorities who abused their power.

"The prosecutor who charged him, the cops who raided him and arrested him — they were all wrong about the law and did real harm to him, and none of them are going to suffer any consequences."

Most police officers told us that they're fine with cameras, and some were happy they were recorded when they were vindicated of misconduct charges thanks to a video made by a bystander. The cops who object tend to be problem cops.

That little phone with a camera is a good thing. Now it's even a weapon against tyranny.

But, Balko added, only if the laws "ensure that we can continue to use it that way."